Dry earth is electrically non-conductive to the extent of being a good electrical insulator. As moisture is added, the earth will become more conductive until it is water-saturated. When saturated, the earth is then highly conductive. The earth's conductivity can be measured and becomes the basis for the moisture control system of the present invention.
When the moisture control of an extensive plot of land is effected by a single control unit, some of the land may be inadequately irrigated while other parts of the plot may be overirrigated and undesirably saturated with water. The present invention provides appropriate irrigation for a plurality of different zones where each zone is irrigated only to the extent as needed.
The presently known prior art consists of the following U.S. Pat. Nos.: 3,823,874; 3,892,982; 3,961,753; 4,014,359; 4,122,389; 4,246,574; 4,256,133; 4,268,824; 4,304,989; 4,514,722; 4,545,396; 4,548,225; 4,646,224; 4,657,039; 4,683,904; 4,684,920; and 4,693,419.